1868.] Mr. C. Chambers on Magnetic Declination at Bombay. 161 



II. " On the Solar and Lunar Variations of Magnetic Declination at 

 Bombay." — Part I. By Charles Chambers, Esq., Superin- 

 tendent of the Colaba Observatory. Communicated by B. 

 Stewart, LL.D. Received June 30, 1868. 



(Abstract.) 



The hourly observations of magnetic decimation at the Government Ob- 

 servatory, Bombay, have extended over a period of nearly a quarter of a cen- 

 tury, but the present discussion is confined to the observations made in the 

 seven years 1859 to 1805. After describing the instrument with which the 

 observations were made and the method of reducing them, the writer ex- 

 hibits, by means of Tables and curves, the following results : — 



1st. The agreement of the diurnal variation of the aggregate of easterly 

 disturbances when different separating values are adopted. 



2nd. The same for the aggregate of westerly disturbances. 



3rd. The diurnal variation of the aggregate of easterly disturbances, ex- 

 ceeding l'*4 in amount, in the period of seven years. 



4th. The same for westerly disturbances. 



5th. The disturbance-diurnal variation, or the excess at each hour of the 

 aggregate of easterly over the aggregate of westerly disturbances. 



6th. The aggregates of easterly, westerly, and easterly and westerly dis- 

 turbances, and the numbers of disturbed observations in each month of the 

 year. 



7th. The aggregates of easterly, westerly, and easterly and westerly dis- 

 turbances, and the numbers of disturbed observations, in each of the years 

 1859 to ] 865, and in the period of seven years. 



8th. The solar- diurnal variation of decimation in each month of the 

 year, and for the whole year. 



9th. The excess of the diurnal variation of declination for each month 

 over the mean diurnal variation for the year. 



10th. The mean diurnal variation of declination for the half-years April 

 to September and October to March, in each of the years 1859 to 1865. 



1 1th. The semiannual inequality in the mean diurnal variation of decli- 

 nation. 



1 2th. the mean diurnal variation of declination for each of the years 

 1859 to 1865. 



13th. The calculated values of the coefficients A x , B x , A 2 , B 2 , A 3 , and B 3 

 in- the equation 



% h =A 1 cos n + B x sin n + A 2 cos 2n + B 2 sin 2n + A 3 cos3n + B 3 sin 3n + &c. . . » 

 which expresses the mean diurnal variation of declination for each month 

 of the year, for the whole year, and for different half-years. 



14th. The same for the half-years- April to September and October to 

 March, in each of the years 1859 to 1863. 



15th. The solar-diurnal inequality of declination, in the calculation of 

 which all disturbances are included. 



